They say the advantages are that smaller scale storage systems are feasible, and that the cost will be much lower. I see a number of problems, though.

There are only a limited number of locations where pumped storage will work well, because you need the high and low pools to be close together for the pipe resistance to be acceptable. For places with a lower gradient between the high and low locations, running large masses up and down rails might be a good choice. Rails can operate will pretty low rolling losses, so a rail based system to raise and lower cheap rough and ready blocks might work out well. The system Energy Vault is proposing goes to the opposite extreme - a 100% gradient, lifting blocks vertically, to build a tower, by stacking them. This looks nice in the video, but I suspect reality will bite. A practical system needs to work in strong winds, which will make it difficult to place blocks on long cables precisely. The system requires that many blocks be stacks up, because they won't get much potential energy stored in a low stack. Even with a really tall stack, the lower blocks in the stack won't be storing much energy. A tall stack would require precisely shaped blocks, precisely positioned, if the stack is to remain stable. Over time, how would they keep the blocks in pristine condition to fulfil this requirement?

Here's a podcast discussing an alternative to the concrete or to pumped hydro(Omega Tau – Gravity Storage (http://omegataupodcast.net/299-gravity-storage/)). They say about the concrete-block approach that this potentially require much maintenance. Because lots of mechanics that could wear. One of the pro side is that even 'small' Installations seems to be possible.

If the Gravity Storage is a viable solution I'm not sure either. But it's an interesting approach as well.

Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

Thought of exactly the same, but haven't bothered doing any ballpark maths. Thanks for that, it is evident now ;)

Way back in the day, before electrical power of any scale was really practical, the dock at Liverpool had a clever hydraulic energy storage scheme for operating its cranes and winches.

It looked kind of like pumped storage writ small, but with the trick that the accumulator towers were really giant hydraulic rams that lifted large weights to allow high working pressures without needing the towers to be overly high... Prime power was steam plant in a few engine house locations around the dock.

Did it work? Yes, it did, but it was far more about peak power demand then bulk energy storage, and we have easier ways to do that today.

Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

A pyramid has an centre of gravity which is intentionally low. This is evidenced by it only being at a quarter height. I'm not saying there aren't issues with the technology, but it's not the best example.

Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

A pyramid has an centre of gravity which is intentionally low. This is evidenced by it only being at a quarter height. I'm not saying there aren't issues with the technology, but it's not the best example.

So, you think the pyramid designers thought "let's make a monument with a really low C of G"? :-\

It would be easier to assemble and disassemble a pyramid every day, as its shape greatly eases the precision requirements for the blocks and their placement.

I saw someone call into question the wear and tear of the cables hauling the blocks. That's not a factor I had considered, since many elevators are used continuously through the waking hours, and the cables seem to last for years.

So, you think the pyramid designers thought "let's make a monument with a really low C of G"? :-\

It would be easier to assemble and disassemble a pyramid every day, as its shape greatly eases the precision requirements for the blocks and their placement.

I saw someone call into question the wear and tear of the cables hauling the blocks. That's not a factor I had considered, since many elevators are used continuously through the waking hours, and the cables seem to last for years.

A pyramid is a relatively stable shape. The Egyptians were a fairly clever lot, so you can bet they realized a pile of sand settles in pretty much that shape because it's quite stable.

A pyramid wouldn't be a good shape to use for this, exactly because its centre of gravity is too low. You'd be moving around a huge pile of material for not that much energy stored. That's not what you want. I don't see how the shape eases requirements. Interlocking blocks should be self centring when they're placed with a modicum of precision. You can basically build any shape you like, but getting more blocks high up increases the energy stored. This means you probably want to build as high as you can without things becoming too unstable.

Right, the Taum Sauk plant in central Missouri puts 1.5 billion gallons (12 billion Lbs or 6 million tons) of water up on an 800 foot mountain. Because the pipes are small, and the reservoir is big, basically all the water starts at the 800 foot elevation. This tower scheme seems to waste a lot of the blocks building the BOTTOM of the tower, where the potential energy is low.

A pyramid is a relatively stable shape. The Egyptians were a fairly clever lot, so you can bet they realized a pile of sand settles in pretty much that shape because it's quite stable.

A pyramid wouldn't be a good shape to use for this, exactly because its centre of gravity is too low. You'd be moving around a huge pile of material for not that much energy stored. That's not what you want. I don't see how the shape eases requirements. Interlocking blocks should be self centring when they're placed with a modicum of precision. You can basically build any shape you like, but getting more blocks high up increases the energy stored. This means you probably want to build as high as you can without things becoming too unstable.

The pyramid shape eases requirements, because any old blocks will stack up to make a stable pyramid. They don't need to be made very precisely, and as they suffer bumps and bruises they would still be just fine for the job. To make a tall, narrow, and not very stable tower the blocks need to be precise, and even small amounts of wear and tear will be problematic.

I saw someone call into question the wear and tear of the cables hauling the blocks. That's not a factor I had considered, since many elevators are used continuously through the waking hours, and the cables seem to last for years.

Nope, they have to be replaced annually in anything that lifts people, or lifts things that could conceivably go over people's heads (cranes, etc.) At least that's true in the US.

I doubt lift ropes are replaced annually. In fact I have never seen any mentioning of any lift being out of service due to rope change out. I am pretty sure they does not have to be replaced annually. The wear on them is quite minimal I'd guess and there are humongous safety margins in place.

But there may be different standards in place in different countries. Maybe in the US, when they go on cheap, lifts aren't designed with such brutal safety margins and hence why the replacements required. :-//

The pyramid shape eases requirements, because any old blocks will stack up to make a stable pyramid. They don't need to be made very precisely, and as they suffer bumps and bruises they would still be just fine for the job. To make a tall, narrow, and not very stable tower the blocks need to be precise, and even small amounts of wear and tear will be problematic.

Again, with a minimum of thought you can make blocks that can be banged up quite a bit before that start being an issue. You don't want to throw away half of the power potentially stored because you're worried about wear. Modern technology should be able to place them accurately enough for that not to be an issue, even if the blocks aren't shaped to prevent the issue.

The pyramid shape eases requirements, because any old blocks will stack up to make a stable pyramid. They don't need to be made very precisely, and as they suffer bumps and bruises they would still be just fine for the job. To make a tall, narrow, and not very stable tower the blocks need to be precise, and even small amounts of wear and tear will be problematic.

Again, with a minimum of though you can make blocks that can be banged up quite a bit before that start being an issue. You don't want to throw away half of the power potentially stored because you're worried about wear. Modern technology should be able to place them accurately enough for that not to be an issue, even if the blocks aren't shaped to prevent the issue.

OK. Apply a minimum of "though" and see if you can propose a design that might work.

Try stacking those 150m high, when they start to get beaten up a bit, and see how far the stack tilts.

You only need to get to 75 metres for the same amount of energy stored, as the centre of mass is in a much more favourable position. As long as they're somewhat clean there shouldn't be tilting issues. If it somehow does turn out to be an issue, automated compensation isn't beyond today's technology.

Try stacking those 150m high, when they start to get beaten up a bit, and see how far the stack tilts.

You only need to get to 75 metres for the same amount of energy stored, as the centre of mass is in a much more favourable position. As long as they're somewhat clean there shouldn't be tilting issues. If it somehow does turn out to be an issue, automated compensation isn't beyond today's technology.

The proposed design that started this discussion has towers at least 150m tall.

Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

A pyramid has an centre of gravity which is intentionally low. This is evidenced by it only being at a quarter height. I'm not saying there aren't issues with the technology, but it's not the best example.

I just wanted to palce the claim into context. To give it some scale. This is also what I've found:"San Francisco use about 6,500 MWh daily with around 800,0000 residents."So assuming that it is to store solar power, you would need to build 100 towers to make it through the night. And it has so many moving parts, that make it really unreliable.

I think the clear way to store energy is Power to gas (LNG). The round trip efficiency is not that great at the moment, at around 75%, but that is not important*. Storing gas is a solved problem. 1 cubic meter of LNG is about 600 cubic meter of natural gas, about 6000KWh. In a 30 foot container that is about 200MWh, or 8 of these towers. The entire concept is just silly if you compare it. (https://upload.wikimedia.org/wikipedia/commons/thumb/2/20/Methanier_aspher_LNGRIVERS.jpg/600px-Methanier_aspher_LNGRIVERS.jpg)This is 135000 cubic meter, or about 810000 MWh, enough to power the SF for 4 months.

*What is important is the total system cost. If you spend 2 EUR (including amortization) storing 1 EUR worth of electricity, you are doing it wrong**. What matters is the electricity cost at night. You can overcome efficiency problem with "just" more solar power. ** That is why the ie powerwall is a futile concept. It costs more to store the electricity than to buy it.

Hang on -- I may be missing something here. LNG is Liquefied Natural Gas. The actual power (eventually used for heating, generating electricity etc.) comes from the natural gas, i.e. a fossile fuel, right?

One applies additional energy to liquidify it -- but that is not to store that additional energy, but just to make the natural gas more compact for transportation?

I may have this wrong, in which case, please correct me. Otherwise, while liquefied gas certainly has its uses, you seem to mention it in an incorrect context here: It is not used to store electrical energy, generated from wind or solar.

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.Power to gas (P2G) is not done in the industrial scale, but there is a 100 MW plant being built in Germany. I think others will follow. And methane can be used in many other ways than just power generation. My favorite part about P2G is that it is actually reverses the CO2 emissions and global warming.

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.

Ah, thanks. So it's not about LNG, but about synthesizing gas using electrical power. The synthesized gas may or may not be liquefied afterwards (if it is, that does not store further electrical engergy). And the tanker ship full of LNG which you showed is rather unrelated to this proposal for the storage of electrical energy, right?

Way back in the day, before electrical power of any scale was really practical, the dock at Liverpool had a clever hydraulic energy storage scheme for operating its cranes and winches.

It looked kind of like pumped storage writ small, but with the trick that the accumulator towers were really giant hydraulic rams that lifted large weights to allow high working pressures without needing the towers to be overly high... Prime power was steam plant in a few engine house locations around the dock.

Did it work? Yes, it did, but it was far more about peak power demand then bulk energy storage, and we have easier ways to do that today.

Regards, Dan.

You could visit https://en.wikipedia.org/wiki/Hydraulic_engine_house,_Bristol_Harbour (https://en.wikipedia.org/wiki/Hydraulic_engine_house,_Bristol_Harbour) and also see the forerunner of all modern ships https://www.ssgreatbritain.org/ (https://www.ssgreatbritain.org/)

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.

Ah, thanks. So it's not about LNG, but about synthesizing gas using electrical power. The synthesized gas may or may not be liquefied afterwards (if it is, that does not store further electrical engergy). And the tanker ship full of LNG which you showed is rather unrelated to this proposal for the storage of electrical energy, right?

The point is that we can store massive amount of LNG and it is probably the cleanest thing to burn. There is already a gas network built up and we use a lot for heating. Power plants are there and transportation can be converted to use it. Not just cars, but cargo ships for example. So there is infrastructure to use it, and we have the means to generate it, and store it.And CO2 scrubbing is possible. It might be "more expensive" than other methods, but the point is that the cost is energy. All these problems can be offset by just installing more panels.

So you pyrolyze wood to make wood gas, burn that gas to get CO2, then invest energy to make methane which you can burn later on? Well sure, but why not use wood and wood gas directly?

Because using wood that way isn't "renewable"/"CO2 neutral" according to the climate agreements?

Actually, wood isn't very compact, so converting the wood gas to methane (which is already widely used in e.g. buses) would be simply a fuel refinement process.

I do know that CO2 sequestration from ambient air is nontrivial, and typical concentrations (0.04% per volume) are so low that the methane-generating processes cannot realistically rely on CO2 from ambient air.

Once exporting begins - it seems to me that a country now has to allow it - to the higest bidder, not to any favored group, like their own people, regardless of its impacts. It likely wouldnt matter where it came from, cutting down living forests to create wood gas may seem like a bad idea to us but that doesnt likely matter, just sayin.

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.

Ah, thanks. So it's not about LNG, but about synthesizing gas using electrical power. The synthesized gas may or may not be liquefied afterwards (if it is, that does not store further electrical engergy). And the tanker ship full of LNG which you showed is rather unrelated to this proposal for the storage of electrical energy, right?

The point is that we can store massive amount of LNG and it is probably the cleanest thing to burn. There is already a gas network built up and we use a lot for heating. Power plants are there and transportation can be converted to use it. Not just cars, but cargo ships for example. So there is infrastructure to use it, and we have the means to generate it, and store it.And CO2 scrubbing is possible. It might be "more expensive" than other methods, but the point is that the cost is energy. All these problems can be offset by just installing more panels.

Compressed sawdust brickets are actually really good for heating; beats typical firewood in energy density easily. (Anecdotal evidence only, but from a large house well north of Arctic Circle.)

Unsurprisingly, the main problem is manufacturers "accidentally" include quite a bit of sand and other non-burning debris in their brickets. There is a significant difference between manufacturers and even batches; some produce a lot of ashy sand when burnt. (Incomplete combustion is not the cause; the fireplaces used all had separate incoming cold air inlets beneath the fireplace.)

Sawdust/pellets are of course quite widely used for heating already, and are surprisingly clean tech (as long as good combustion is achieved). Wood gas is even cleaner, though.

The video of the tower certainly looks nice ... but I don't think it quite makes sense.

Each block stores a potential energy based on it's starting height and ending height. in other words, energy increases with each layer of the tower:Blocks at ground level store no energy.Blocks at the top of the tower store the most energy.

So it actually stores quite a bit less energy then "first glance" might make you think (all those blocks)...

The video shows it basically building a wall around itself as it moves blocks from the top of the tower to the wall - but with each layer, the amount of energy retrieved lessens because the top of the tower is getting lower and the wall is getting higher.

The crane seems to have quite a long reach, and assuming the support structure is in place, counterweight would not be a problem as you could move the blocks in opposing pairs... so wouldn't it make sense to be building a large flat disk around the tower and not a wall?

Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

Just checking that it looks like you may be out by an order of magnitude. Apparently the pyramid masses approximately 5,200,000 tonnes.

So somebody found some footage of a gravel mine and made a bollocks story around it.[sigh]Efficiency of such a conveyor will be horribly low, and maintenance costs high. Far to many moving parts.

Churchbells have been driven for centuries on similar systems.There have been some attempts by using a railroad track on a hill but pumped hydro is much simpler if you can find convenient places to store your water.

So you pyrolyze wood to make wood gas, burn that gas to get CO2, then invest energy to make methane which you can burn later on? Well sure, but why not use wood and wood gas directly?

Because using wood that way isn't "renewable"/"CO2 neutral" according to the climate agreements?

Actually, wood isn't very compact, so converting the wood gas to methane (which is already widely used in e.g. buses) would be simply a fuel refinement process.

I do know that CO2 sequestration from ambient air is nontrivial, and typical concentrations (0.04% per volume) are so low that the methane-generating processes cannot realistically rely on CO2 from ambient air.

Wood gas doesn't contain much CO2. It's mostly CO, H2, with a little CH4 and small amount of CO2. It can become unstable at high pressures, so needs to be converted to pure CH4, which is more than a bit than scrubbing and does involve some losses.

Whether it's renewable or carbon neutral or not, depends on how it's produced. It's ultimately more efficient to use solar panels and store the energy in pumped water.

Gasification is a good idea though and can be used to convert dry, organic waste such as nut shells or corn cobs, to a fuel which can be burnt to produce heat and electricity.

A pyramid is a relatively stable shape. The Egyptians were a fairly clever lot, so you can bet they realized a pile of sand settles in pretty much that shape because it's quite stable.

The Egyptians were clever enough for trial and error without testing; their first pyramids collapsed.

https://en.wikipedia.org/wiki/Bent_Pyramid

In 1974 Kurt Mendelssohn suggested the change of the angle to have been made as a security precaution in reaction to a catastrophic collapse of the Meidum Pyramid while it was still under construction.

Gasification is a good idea though and can be used to convert dry, organic waste such as nut shells or corn cobs, to a fuel which can be burnt to produce heat and electricity.

Wood gas was widely used in cars during the second world war in this part of the world, due to fuel shortages. The downside was the size of the fuel, really, because the wood gas was generated in situ as needed. (In particular, that cylinder/"tank" you see in those vehicles is the generator; the gas itself is not stored at all.)

If, for some reason, we absolutely had to stop using gasoline and diesel for vehicles, switching to wood burning would not be that big of an issue. "Mad Max" simply would not happen anywhere you got trees aplenty; people would just tinker a bit with their cars, add funky silly-looking gasification canisters, and go on with their lives. Like they did here in Fennoscandia during the second world war. Fuel use for a practical four-door sedan is 50 - 100 kg of firewood per 100 km travelled.

That said, you can burn even trash for heat and energy just fine. Just look at Sweden (https://www.nytimes.com/2018/09/21/climate/sweden-garbage-used-for-fuel.html), for example.

Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

Just checking that it looks like you may be out by an order of magnitude. Apparently the pyramid masses approximately 5,200,000 tonnes.

My first though after seeing that was how would that system behave if there's powerful gusts of wind?

These may be used near wind turbine parks which obviously are in areas with wind.

What happens when one of those bricks is going down and suddenly there's powerful wind which starts moving the brink sideways as it goes down? Looks to me like those bricks must be accurately be placed down and lock together somehow to prevent them from falling off or losing the overall integrity.

Another downside of wood gas (and producer gas) is that the CO content makes it deadly. The whole thing about someone committing suicide by putting their head in their oven comes from wood gas and it was a major reason to replace it with natural gas.

Another downside of wood gas (and producer gas) is that the CO content makes it deadly.

Yup, carbon monoxide being odorless, tasteless, and slightly lighter than air makes it easy for one to die accidentally from it. (We have carbon monoxide detectors in all rooms with a fireplace for exactly that reason, and smoke detectors in other rooms.)

In vehicle use it was not a problem, because the amount of wood gas at any given point was very small: no tank, the gas was being produced as needed. That said, I would *not* want to have a vehicle, or anything, with a tank for wood gas or producer gas, even if they were to add mercaptan or other odorants to detect leakage. Too dangerous. (However, I still think using wood, and wood gas as a precursor for better/safer fuels, like liquefied natural gas, makes sense even if some energy is wasted in the production.)

Let's do back of the envelope calculations:Great Pyramid of Giza weights 500.000 tonnes. It is 146 meter high. It's center of gravity is at 1/4 of it's hight, 36m. It's potential energy is about 50 MWh.These guys claim that they can store 35MWh in their tower. Basically claiming that they can build the pyramid in a day and take it apart at night.

Just checking that it looks like you may be out by an order of magnitude. Apparently the pyramid masses approximately 5,200,000 tonnes.

Power to gas uses power to do this reaction:2 CO2 + 4 H2O = 2 CH4 + 3O2Natural gas is mostly methane.Power to gas (P2G) is not done in the industrial scale, but there is a 100 MW plant being built in Germany. I think others will follow. And methane can be used in many other ways than just power generation. My favorite part about P2G is that it is actually reverses the CO2 emissions and global warming.

Oh so you mean make wood gas, burn it, presumably to generate energy and use that to convert the CO2 generated and water to methane and oxygen? That would result in less energy than simply burning the wood gas in the first place, as it will take energy to convert the CO2 to methane.

Gasification is a good idea though and can be used to convert dry, organic waste such as nut shells or corn cobs, to a fuel which can be burnt to produce heat and electricity.

Wood gas was widely used in cars during the second world war in this part of the world, due to fuel shortages. The downside was the size of the fuel, really, because the wood gas was generated in situ as needed. (In particular, that cylinder/"tank" you see in those vehicles is the generator; the gas itself is not stored at all.)

If, for some reason, we absolutely had to stop using gasoline and diesel for vehicles, switching to wood burning would not be that big of an issue. "Mad Max" simply would not happen anywhere you got trees aplenty; people would just tinker a bit with their cars, add funky silly-looking gasification canisters, and go on with their lives. Like they did here in Fennoscandia during the second world war. Fuel use for a practical four-door sedan is 50 - 100 kg of firewood per 100 km travelled.

That said, you can burn even trash for heat and energy just fine. Just look at Sweden (https://www.nytimes.com/2018/09/21/climate/sweden-garbage-used-for-fuel.html), for example.

Yes, wood gas used in the war, instead of petrol to power cars, but not very many people had cars back then. It's impractical to use on a large scale and is very inconvenient. The wood gas generator needs to be fired up for awhile before starting the car and properly shut down afterwards, making it unsuitable for short journeys. We'd soon run out of trees, as there aren't enough of them to use sustainably. It would make far more sense to go electric instead. Modern gasification technology can convert wood, waste biomass and hydrocarbons to electricity much more efficiently, than vehicle mounted wood gas generators.

Burning biogas will give less energy, than just burning the rubbish, since only biodegradable material will produce methane and burning the rubbish will use all of the organic material. The only advantage of biogas is it doesn't release so much carbon dioxide, as the carbon in the buried non-biodegradable matter remains their for all eternity.

Burning biogas will give less energy, than just burning the rubbish, since only biodegradable material will produce methane and burning the rubbish will use all of the organic material. The only advantage of biogas is it doesn't release so much carbon dioxide, as the carbon in the buried non-biodegradable matter remains their for all eternity.

Burning the rubbish requires complex capture mechanisms to avoid a whole bunch of nasty things in the trash being emitted from the flue, so there is a tradeoff.

Burning biogas will give less energy, than just burning the rubbish, since only biodegradable material will produce methane and burning the rubbish will use all of the organic material. The only advantage of biogas is it doesn't release so much carbon dioxide, as the carbon in the buried non-biodegradable matter remains their for all eternity.

Burning the rubbish requires complex capture mechanisms to avoid a whole bunch of nasty things in the trash being emitted from the flue, so there is a tradeoff.

Biogas also requires scrubbing before it can be burnt to produce energy.

Gasification can also be used, rather than simply burning the rubbish, as it's easier to clean a smaller volume of producer gas, than a larger volume of flue gas.

Taking gas from landfill and extracting the biogas or burning/gasifying all the rubbish are both sub optimal. The waste should be separated into recyclable, biodegradable and non-biodegradable first. The biodegradable waste is then better fermented to produce biogas and fertiliser and the non-biodegradable waste gasified to produce electricity and heat.

Oh so you mean make wood gas, burn it, presumably to generate energy and use that to convert the CO2 generated and water to methane and oxygen? That would result in less energy than simply burning the wood gas in the first place, as it will take energy to convert the CO2 to methane.

Yes. The issue is that you don't want to store wood gas.

In the vehicles where wood gas was used, it was produced as needed, not stored. The production process wastes about 30% of the energy in the wood.

Yes, wood gas used in the war, instead of petrol to power cars, but not very many people had cars back then.

About 46 000 between 1939 and 1946 in Finland, for a population of about 3.6 million.

I am kind of inclined to argue that people already have too many cars, so that if a sudden shift away from petrol were to occur, it would mostly be a shift away from personal cars, and not so much a shift away from transportation in general. Buses, not Mad Max.

Why has no one mentioned the ramp rates when comparing potential energy storage to chemical energy storage?

Potential energy generally has a much faster ramp rate than chemical. Open the dam and the turbine output ramps up way faster than turn up the heat and wait for boiler to heat up.

Around 5pm when solar panels stop generating and people arrive home, plug in their cars and cook dinner, the amount of stored energy that needs to be converted to electricity ramps up quickly. The more solar we have and the more electric cars we have, the bigger problem we have (in regards to utilities providing stable voltages).

If utilities have access to potential energy storage then they should be more accepting of electric vehicals and renewables and their inconsistent, unreliable usage.

Utilities that rely on chemical energy burn off a lot of energy when loads are low just so they are ready for when loads are high.

A fast start on a combined cycle turbine is actually very efficient as long as you then keep it running for long enough to get meaningful power out of the steam part of the cycle.

In fact the part of the cycle where you are recovering heat into basically cold water in the steam generator is actually the most efficient part, it is just that you cannot get that energy back until you have run long enough to get reasonable steam pressure.

Where those things suck is "startup, run for an hour, shutdown" because the heat recovery cycle does not have time to warm up to produce reasonable amounts of power, you loose the energy stored in the boiler when you shutdown for obvious reasons.

This actually makes a combined cycle gas turbine a reasonable choice for a spinning reserve as it throttles quickly and as long as idle is sufficient to keep the steam generator warm...

OK. Apply a minimum of "thought" and see if you can propose a design that might work.

This or a variant of it self centres when roughly placed and is already designed to be hard to break and fit while worn.

Try stacking those 150m high, when they start to get beaten up a bit, and see how far the stack tilts.

They look like giant concrete lego blocks. I'm imagining it'll nest decently into recesses in the bottom... That said you could minimize potential for breaking and such by having a hole in either side and running a cable through them to help keep them straight and lined up.

Might be better to have a metal shell on the outside as concrete/cement is prone to chipping. Metal just gets little dings and dents. Would be more expensive but last much longer and still be cheaper than metal blocks while providing a huge amount of weight/mass to store energy with.

One kWh is 3600*1000 joules. You'd need lots of m or lots of h to get one of those from mgh...

In the video they say it can store 30MWh. That's 30e6*3600 joules = mgh => mh = 30e6*3600/9,8 = 11020408163 ergo if it were , say, a 100m tall tower (that's a 33 stories high skyscraper), the mass would have to be (at least) 110204081,63, which is a block of 110204 tons of concrete at a 100 meters high in the sky, with all the 110204 tons at the very top of the tower.

I don't think any potential energy storage system will be able to compete with pumped hydro, either traditional or ocean floor (ie. you pump the water out of a concrete sphere). Solid matter is inconvenient to work with.

Full disclosure: I did not run any numbers on this, I'm away from the computer, but this just entered my mind and can't shake it. Consired this a runaway train of thought.

What if the system is inverted and under sea? Anchor it to the seabed and have big steel baloons tied by cables to the winch at the bottom (or have a pulley and the winch with the generator on shore).Sea is fairly calm once you go deeper than 20 m, but there are currents to consider. Oil rigs have that solved. I suppose some type of control surfaces could be employed to help with position control by taking advantage of up/down movement.Big military submarines reach couple of hundred meters regularly.What do you think?

A big concrete block should be much cheaper to make than a big hollow sphere that has to withstand significant pressure, especially if you want to pull it deep down to store lots of energy. If you need one winch per sphere, or some tricky mechanism to switch spheres over between the winch/generator and some ground anchors, that adds to the complexity. Stacking blocks and relying on gravity to ensure they stay where they are seems simpler.

There was an odd proposal out there to build concrete spheres to sink to the ocean and pump water in an out. However this is not much different than building small dams the size of spheres, just under water and the other way around. Small installatons suffer from too many pipes / pumps. Things like motors/generators tend to be higher efficiency if larger. Actually moving things under water adds trouble with cables.

Stacking blocks sound simple, but pumping water is even simpler (if one has a suitable mountain). A ton of concrete in a damm can easily hold back more than 1 ton of water.

On the other hand the underwater solution doesn't need a high flow pipeline. You pump water a couple of meters, yet with the same pressure difference as a mountain based system with a long pipeline between the reservoirs.

Fraunhofer institute estimated they could do it cheaper than pumped hydro up a mountain.

Underwater systems have the added benefit that they are a lot less dangerous. A huge concrete sphere accidentally "falling" underwater if anything breaks will make a lot less harm than its open-air counterpart.

A big concrete block should be much cheaper to make than a big hollow sphere that has to withstand significant pressure, especially if you want to pull it deep down to store lots of energy. If you need one winch per sphere, or some tricky mechanism to switch spheres over between the winch/generator and some ground anchors, that adds to the complexity.

Yeah, it would be more expensive to make the steel sphere, especially since you also need the anchor.Regarding the pressure, wouldn't pressurizing the sphere at to half the design depth pressure help?There is still metal fatigue to consider. How many times can the device be subjected to pressure changes before welds fail? I tried looking up that number for real world submarines, but was not able to find an instance where it is mentioned how many dives a sub had before decommissioning, or if it's even a consideration. I suppose that would be classified.

Fatigue and fatigue related impact on overall efficiency might be the biggest concern about this - next to the amount of CO2 produced just for the concrete and the unused energy in start and stop of the motion... No doubt that there could be a working prototype, but this is really about longevity and which efficiency is acceptable for a storage concept; i would not operate this in an area with earthquakes or high wind.

It would not even need to be a freestanding tower, something similar could be installed in closed mines under ground, which do have longer slopes or elevator shafts. It might not be as many and rather small, but longer distances and higher weight would be possible, as there is a support structure enabling some safety features in case of a failure. The longer distance would offset the problem with losing to much potential energy through stacking next to a very limited height of a freestanding tower.

There are other similar concepts, like lifting weights with water pressure to store energy using conventional pumps and turbines. The weight could be locked in place and it would mean less moving (wear)parts, plus the benefits of a mass with higher density than water in the system and a lower loss by hydraulic control. This could shrink the required volume for a pumped storage hydroelectric plant by the difference in density of all media used and enable to use it in places otherwise not suitable.

However, since a few years Power2Gas is the concept that gains a lot of traction here, it uses the natural gas network as storage, small and big installations are in the making and working. Given that gas turbine generators allow a fast start of electricity production and are all over the place to cover shortages, this makes more sense. Not saying it is that easy, because hydrogen penetrates some materials and combustion processes are never fully ideal.

There was an odd proposal out there to build concrete spheres to sink to the ocean and pump water in an out. However this is not much different than building small dams the size of spheres, just under water and the other way around. Small installatons suffer from too many pipes / pumps. Things like motors/generators tend to be higher efficiency if larger. Actually moving things under water adds trouble with cables.

Stacking blocks sound simple, but pumping water is even simpler (if one has a suitable mountain). A ton of concrete in a damm can easily hold back more than 1 ton of water.

Yeah, but in fact you are not pumping water anymore. In a regular " two lake " system, you are pumping water and using a generator. In the sunken bubble, you actually need to pump compressed air, which is much less efficient. Not to mention anchoring it down, as others said. I dont know, it seems sketchy. On the other hand Fraunhofer is highly qualified. Do you have a link?

There was an odd proposal out there to build concrete spheres to sink to the ocean and pump water in an out. However this is not much different than building small dams the size of spheres, just under water and the other way around. Small installatons suffer from too many pipes / pumps. Things like motors/generators tend to be higher efficiency if larger. Actually moving things under water adds trouble with cables.

Stacking blocks sound simple, but pumping water is even simpler (if one has a suitable mountain). A ton of concrete in a damm can easily hold back more than 1 ton of water.

Yeah, but in fact you are not pumping water anymore. In a regular " two lake " system, you are pumping water and using a generator. In the sunken bubble, you actually need to pump compressed air, which is much less efficient. Not to mention anchoring it down, as others said. I dont know, it seems sketchy. On the other hand Fraunhofer is highly qualified. Do you have a link?

Any scheme involving compressed gas gets complex, because the energy that goes into storage is a mix of two forms - pressure and heat - and storing heat has inevitable insulation issues if the store is intended to persist for any length of time.

Yeah, but in fact you are not pumping water anymore. In a regular " two lake " system, you are pumping water and using a generator. In the sunken bubble, you actually need to pump compressed air, which is much less efficient.